Distressed cementitous, for example, asphalt and concrete, vehicular supporting surfaces like roads, highways, parking lots, runways and the like have been provided with a new wearcourse by means of a slurry seal technique for many years. This technique, while primarily employed for corrective maintenance of pavment surfaces, has also been used as a preventative measure. In such a technique, aggregate, water and an asphaltic emulsion are combined in a mixer mounted on a moving truck to form a slurry and the slurry is discharged to a spreader box where it, in turn, is discharged, while the truck is continuously moving, to the pavement surface to be treated. A squeegee is usually attached to the spreaderbox to provide a uniform coating on the pavement. The aggregate employed may be calcareous, siliceus or granitic. The size of such slurry seal aggregate as recommended by the International Slurry Seal Association is set forth in A BASIC ASPHALT EMULSION MANUAL prepared by THE ASPHALT INSTITUTE for the UNITED STATES DEPARTMENT OF TRANSPORTATION (FHWA-OIP-79-1) at page 52.
In contrast to a rapid set emulsion which has virtually no ability to mix with such slurry seal aggregate, because of a substantially instantaneous hardening of such mixture, slurry seal compositions typically employ a slow setting emulsion. Those slow set emulsions typically are cationic emulsions and are designed to mix with aggregate and water so as to form a flowable slurry in the slurry-truck mixer which slurry can be readily discharged and dispensed from the spreaderbox onto the pavement to be treated. In order to provide the needed mix time, the slow set emulsions unfortunately also provide the slurry seal composition with a long break time, that is the time for the asphalt and aggregate phase to separate, or break, from the water phase. More recently, quicker setting, slow set emulsions have been finding utility in slurry seal treatment processes and are generally referred to in the trade as a quick set emulsion. Such quicker setting, slow set emulsions, like the older slow set emulsions, also need to have their break time decreased while allowing for adequate mixing time in the mixer of a slurry seal application truck. Additionally, the properties of the asphalt employed in such emulsions need to be improved.
In accordance with the present invention, an asphaltic emulsion is provided which is adapted for use in slurry seal surface treating technology which has an improved break time, that is decreased break times, adequate mixing time in conventional slurry seal equipment and which has improved properties.
Thus, in accordance with the present invention, an improvement in pavement surface treating methods is provided of the type which comprises combining a slow setting asphaltic emulsion and aggregate in a mixer, and while moving the mixer along said pavement to be surface treated, mixing said emulsion and aggregate to form a flowable slurry seal composition and substantially continuously discharging said slurry seal composition onto said pavement whereby the composition breaks and then subsequently cures to provide a traffic resistant surface treatment. The improvement resides in combining with the asphaltic emulsion a rapid setting emulsion containing the reaction product of an acrylamide, asphalt having a viscosity of less than 120,000 cps (at 140.degree. F.), a vinyl aromatic monomer and a rubbery polymer with the rapid setting emulsion being present in an effective breaktime decreasing amount, that is in an amount sufficient to increase the rate at which the emulsion breaks. While the amount of the rapid setting emulsion which is employed will decrease the mixing time it, of course, will be apparent that the material is not added in such quantities as to prevent necessary mixing and the formation of a flowable slurry using conventional slurry seal mixers. The incorporation of the rapid setting emulsion into the slow setting emulsion imparts desirable properties to the slurry seal composition and more specifically, the asphalt components thereof. Such desirable properties include improved coatability of various surfaces, including aggregate, improved adhesion characteristics, less stripping, improved flexibility, particularly at low temperatures, improved strength and toughness, reduced high temperature flow, and increased durability.